Variable speed integrated planer motor assembly

ABSTRACT

The integrated planer motor assembly consists of two parts:  
     a. A integrated planer stator assembly that combines the motors stator coils, biased MR sensors and the motor&#39;s variable speed control IC into a single part using advanced high volume semi-conductor manufacturing processes;  
     b. A planer rotor assembly having a precise planer surface containing the high energy permanent magnet and the ceramic ferrite return structure.  
     The rotor assembly is assembled to the stator assembly using a precision washer to establish the motors small and precise air gap thus maximizing magnetic flux density.

BACKGROUND

[0001] 1. Field of Invention

[0002] This invention relates to a variable speed integrated motorassembly for use in applications where precise and variable speedcapability is essential.

[0003] 2. Description of Prior Art

[0004] DC motors made their introduction into disk drives in the early1980's replacing the more larger and complex AC motors and controllerswith a smaller, lower power, and more cost-effective assembly. Statorcoils are hand or machine wound and then arranged in a circumferentialpattern around the rotors permanent magnets. To sense rotor positionduring operation, multiple Hall probe type sensors, were placed in thestator assembly, that sense the magnetic field intensity in the motorsair gap. To eliminate the cost of the Hall probes a sensor-less typecontrol was implemented using the back EMF generated by the coils todetermine motor speed. The output of either the Hall probes or the backEMF is used by complex external control circuits that applies current tothe stator coils to regulate motor speed and direction.

[0005] This multi-part design is complex, expensive and requires severalvendors to implement the design, i.e., wound stator coils, Hall probesensors and the electronic control circuit usually implemented as anintegrated circuit (IC). This leads to complex packaging solutions, thatare specific to the application, and involves extensive cabling andinterconnections. In addition, the design and implementation is noteasily extended to the markets requiring multi-speed operation.

OBJECTS AND ADVANTAGES

[0006] Accordingly, several objects and advantages of my invention are:

[0007] To provide a parallel rotor-stator assembly, separated by a smalland precise air gap, thus increasing the magnetic flux density (andTorque) in the air gap.

[0008] To provide an integrated stator assembly that includes the statorcoils, magnetic field sensors and control electronics IC.

[0009] To provide a permanent magnet rotor assembly with a lowreluctance magnetic return.

[0010] To provide a variable speed motor that can change speeds rapidlyon command from a host system.

[0011] Further objects and advantages of my invention will becomeapparent from a consideration of the drawings and ensuing description.

DRAWING FIGURES

[0012]FIG. 1 shows the Motors Rotor Assembly.

[0013]FIG. 2 shows the base substrate used to fabricate the statorassembly.

[0014]FIG. 3 shows the biased magnetoresistive (MR) elements of thestator assembly.

[0015]FIG. 4 shows the interconnect pattern of the stator assembly.

[0016]FIG. 5 shows the stator coils of the stator assembly.

[0017]FIG. 6 shows the magnetic flux return pattern of the statorassembly.

[0018]FIG. 7 is the completed stator assembly with control IC and motorshaft attached

[0019]FIG. 8 is the completed planer motor assembly.

[0020]FIG. 9 shows the relationship between torque, current, the statorcoils and the rotor's high-energy permanent magnet.

[0021]FIG. 10 shows the relationship between the stators biased MRelements, the stator coils and the rotors high-energy permanent magnet.

[0022]FIG. 11 is a cross section of the assembled rotor and the statorassembly.

SUMMARY

[0023] In accordance with the present invention a variable speedintegrated planer motor assembly having a planer stator assemblycontaining spiral coils, biased MR sensors, interconnect conductorpatterns and a variable speed motor control IC. The motor's statorassembly is manufactured by a high-volume semiconductor process withhigh yields and reproducibility.

DESCRIPTION—FIGS 1 TO 8

[0024] Rotor Assembly 5

[0025]FIG. 1 shows the front and top view of the motors rotor assembly 5and is fabricated according to the following methods and processes.

[0026] 1. A thin walled bearing sleeve of conductive Zirconia, ZrO₂, 20is bonded to a hot pressed, high saturation magnetization, nickel-zincferrite disk, 15 perpendicular and coplanar to datum C-C.

[0027] 2. A high-energy permanent magnet 10, of anisotropic sinteredneodymium-iron-boron, is bonded to ferrite disk 15 and extends beyondthe face of the ferrite disk 15 by approximately 0.001 inches or less.

[0028] 3. The assembly is now lapped (or ground) to establish the finaldatum C-C perpendicular to the ID diameter of bearing sleeve 20. DatumC-C to be flat to within 0.0001 inches or better.

[0029] 4. Bearings 25 are assembled into the thin walled ceramic sleeve20, with an UV curable adhesive, so that the bearing races are coplanarwith datum C-C and the bearings ID bore is perpendicular to datum C-C.

[0030] 5. The face of the assembly is now coated with a thin (1 micron)layer of aluminum oxide, Al²O³, by a sputtering process to create aprotective barrier for the permanent magnet and ferrite disk.

[0031] 6. The assembly is now magnetized perpendicular to the permanentmagnets face (datum C-C) with alternating segments of opposite polarity.In FIG. 1, The cross-hatched segments are magnetized downward (+) andthe clear segment magnetized upward (−).

[0032] The bearing sleeve is injection molded from a conductive aZirconia (ZrO₂) material and is available in high volume from KyoceraCeramics as well as other manufactures. A typical specification for thematerial in the preferred embodiment is: Density: 6.00 (grams/cm3)Flexural Strength 980 (MPa) Young's Modulus 206 (MPa) ThermalConductivity 6 (W/m*K) Coefficient of Linear Expansion 10.5 (ppm/° C.)Porosity none

[0033] The ferrite disk 15 is a hot pressed nickel-zinc ferrite, havingan approximate saturation magnetization of 5,000 gauss acts as a lowreluctance magnetic return in the final motor assembly. It was precisionmolded, and double sided lapped to precise specifications.

[0034] Stator Assembly 70

[0035]FIG. 2 shows the base substrate 30 upon which the stator assemblywill be fabricated using semiconductor processes and methods. The basesubstrate 30 material is nickel-zinc ferrite, the same material as disk15 of the rotor assemble, which also acts as a low reluctance magneticreturn in the motors magnetic circuit. The base substrate 30 wasmanufactured by a hot pressed molding process ground and lapped to aprecise thickness, flatness and surface finish specification.

[0036]FIG. 3 shows the biased magnetoresistive (MR) elements 40 thatdetect magnetic intensity in the motors air gap to provide electronicsignals that will be used to control the motors speed and direction. TheMR elements can be fabricated with the following materials andprocesses.

[0037] 1. Sputter deposit a thin film of copper (Cu) onto the surface ofbase substrate 30 followed by a film of equal thickness of 80/20nickel-iron (Ni—Fe).

[0038] 2. Apply approximately 1 micron of photoresist.

[0039] 3. Expose with MR mask.

[0040] 4. Develop photoresist and postbake.

[0041] 5. Ion Mill to remove Copper and nickel-iron

[0042] 6. Strip photoresist and clean.

[0043] The copper layer provides the magnetic bias to the adjacentmagnetoresistive nickel-iron film and each film thickness is selected toget the desired resistances and amount of Magnetic bias. This generaldesign was used effectively by IBM to fabricate the multi-channelmagnetic heads on its 3340 tape storage sub-system.

[0044]FIG. 4 shows the copper interconnect pattern 50, which connectsthe biased MR elements and the motor stator coils 35 to the motorcontrol IC 62. The interconnect pattern 50 can be fabricated with thefollowing materials and processes.

[0045] 1. Sputter deposit 1,000 Angstroms of copper (Cu) onto the basesubstrate 30 as a seed layer

[0046] 2. Apply approximately 15-20 microns of photoresist.

[0047] 3. Expose with Interconnect mask.

[0048] 4. Develop photoresist and postbake.

[0049] 5. Electroplate copper to the thickness of the photoresist.

[0050] 6. Strip photoresist and clean.

[0051] 7. Ion mill or sputter etch to remove seed layer

[0052]FIG. 5 shows the spiral stator coils 35 used to provide controlledtorque to the rotor. The Inward radial spokes start a 0° and end at 20°and the outward radial spokes start at 60° and end at 80°. Inward radialspokes are connected to outward radial spokes by hub conductors andoutward radial spokes connected to inward radial spokes by rimconductors. The spiral conductors as shown in FIG. 5 has N turns. Thespiral coils 35 can be fabricated with the following materials andprocesses.

[0053] 1. Sputter deposit 1,000 Angstroms of copper onto the basesubstrate 30 as a seed layer

[0054] 2. Apply 125 microns of photoresist

[0055] 3. Expose with spiral coil mask.

[0056] 4. Develop photoresist and postbake.

[0057] 5. Electroplate copper to a thickness of 125 microns.

[0058] 6. Strip photoresist and clean

[0059] 7. Ion mill or sputter etch to remove seed lay

[0060] A stator coil develops torque according to the followingrelationship:

T=R*Lc*B*I=R*C*N*B*V/R

[0061] Where

[0062] T=Torque (N−m)

[0063] R=mean radius of permanent magnet (m)

[0064] Lc=Length of conductors (m)=C*N

[0065] B=Magnetic field Intensity (Tesla)

[0066] I=Current (amps)=V/R

[0067] N=Number of turns

[0068] C=constant

[0069] V=Supply Voltage (volts)

[0070] R=stator coil resistance (ohms)

[0071] Recent advances in UV lithography, thick photoresist, andelectroplating make possible thick conductors (greater than 100microns), narrow width, high edge steepness (>88°) and aspect ratios ofup to 10:1. This means for a 125 micron thick conductor its width can beof the order of 12.7 microns with spaces between conductors of 12.7microns thus maximizing N and minimizing R for the spiral coil. Thisallows the motor to be driven from as low as a 3.3-volt supply withexcellent performance and power dissipation.

[0072] An excellent article entitled “UV Lithography with ThickPhotoresist and Galvanic Moulding” by Dr Bernd Loechel can be viewed onthe Carl Suss web site www.suss.com.

[0073]FIG. 6 shows the magnetic flux return 38 of the stator assembly.It's purpose is the minimize the reluctance of the magnetic flux circuitso as to maximize flux density circulating in the motors air gap thusmaximizing the motors torque. It can be fabricated as follows.

[0074] 1. Sputter deposit 1,000 Angstroms of nickel-iron (Ni—Fe) havingan iron content between 50-55 percent onto the base substrate 30.

[0075] 2. Apply photoresist to a thickness of 125 microns

[0076] 3. Expose with magnetic flux return mask.

[0077] 4. Develop photoresist and postbake.

[0078] 5. Electroplate Ni—Fe with an iron content between 50-55 percent.

[0079] 6. Strip photoresist and clean.

[0080] 7. Ion Mill or sputter etch to remove seed layer.

[0081] A protective coating of a photoresist is applied over the surfaceof the substrate 30 to level and provide support to the 3-D structures.

[0082] 1. Apply photoresist

[0083] 2. Expose with overcoat mask with IC contacts via's

[0084] 3. Develop photoresist and postbake.

[0085] 4. Hard-bake photoresist

[0086] 5. Apply solder, into via's, with silkscreen solder mask.

[0087]FIG. 7 shows the completed Stator assembly 70. A Zirconia shaft 60has been bonded to the Base Substrate 30 using a high strength UVcurable adhesive. The motor control IC bumped die has been attached tointerconnect pattern 50 by a solder re-flow process.

[0088]FIG. 8 is the completed motor assembly 100 and is assembled asfollows:

[0089] Precision spacer 68, is placed over shaft 60, and has a thicknessof:

t _(s) =t+l _(g)

[0090] where

[0091] t_(s)=thickness of precision spacer 68 (m)

[0092] t=thickness from base substrate 30 to top of protective coating(m)

[0093] lg=desired length of air gap (m)

[0094] Rotor assembly 5 is now assembled onto shaft 60 and secured bywasher 67. Washer 67 is bonded to shaft 60, while maintaining properbearing pre-load, with an UV curable adhesive.

OPERATION—FIGS. 9 TO 11

[0095] The relationship between torque, the magnetization of thepermanent magnet 10, and the stator coils are shown in FIG. 9. Salientfeatures are;

[0096] 1. In the preferred embodiment, Spiral coil 1 has inward radialconductors lying between 0° and 20°, outward radial conductors lyingbetween 60° and 80°. Spiral coil 2 has inward radial conductors lyingbetween 240° and 260°, outward radial conductors lying between 180° and200°. Inward to outward radial conductors are connected by hub circularconductors having radius's less than R1 and outward to inward radialconductors are connected by rim circular conductors having radius'sgreater than R2. The coil terminates midway on the last rim conductorand then is connected to the start of the inward conductors of coil 2.Each coil contains N turns. Therefore the length of conductors, withinthe magnetic field having magnetic intensity B, is;

Lc=4*N*(R2−R1)

[0097] 2. The permanent magnet has been magnetized into 3 segmentsaccording to the following table. Angle-degrees 0-60 60-120 120-180180-240 240-300 300-360 Magnetization Tesla +B −B +B −B +B −B

[0098] 3. The torque generated by the coils and applied to the rotor is;

T=Rm*B*Lc*I

[0099] T=Torque (newton-meters)

[0100] R_(m)=R1+((R2−R1))/2) (meters)

[0101] B Flux Density in Air Gap (tesla)

T=((R2−R1)/2+R1)*(4*N*(R2−R1))*B*I

[0102] 4. IC 66 supplies a positive voltage, +V, to the start of coil 1,a positive current, I+, flows through both coils and this creates apositive torque, T+, applied to the rotor and when the current isreversed, −I, the torque is reversed. The amount of voltage supplied byIC 66 to the coils is controlled by a 14-bit DAC.

[0103]FIG. 10 shows the relationship between the biased MR elements 40,the stator coils 35 and the permanent magnet 10.

[0104] 1. The MR elements are biased to −B shown in FIG. 10. MR1 is 120°from the leading edge of the inward conductors of coil 1 and MR2 is 20°from MR1.2.

[0105] 2. The output of the MR elements reflects the polarity of themagnetic field in the air gap. When the magnetic field intensity B isequal and opposite to the MR bias, the output of the MR elements will gohigh. When the magnetic field intensity B is the same as the MR bias,the output will remain low. The waveforms Mr1 and Mr2. are shown in FIG.10 as a function of rotor rotation.

[0106] 3. Gate 1 is high when Mr1 and Mr2 are high and Gate 2 is highwhen Mr1 is low and Mr2 is high. The waveforms Gate 1 and Gate 2 areshown in FIG. 10 shows as a function of rotor rotation.

[0107] 4. The current-torque relationship is; Gate Current I Torque 1Positive Positive 1 Negative Negative 2 Negative Positive 2 PositiveNegative

[0108] 5. Comparing the actual time of a Mr1 cycle, Ta, with the desiredtime, Td, generates a digital error signal.

Error=e=Td−Ta

[0109] 6. Current is then supplied to the coil proportional to themagnitude and sign of the error.

Torque=f(magnitude and sign of the error)

[0110] 7. The system operates in a linear mode with current to the coilvarying from 0 to Imax in 2¹⁴ increments.

[0111]FIG. 11 shows the magnetic flux circulation in the rotor-statorassemblies. To calculate the flux density Bg in the air gap we assumethat there is no magnetic potential drop across the ferrite returns 15,30, and 38. Therefore, the magnetic potential, produced by the permanentmagnets, diminishes solely across these air gap, i.e., Hmlm=Hglg and themagnitude of the flux density in the air gap can be estimated by:

Bg=(lm/(lg)×Hm

[0112] Where

[0113] lm=length of magnet (meters)

[0114] lg=length of air gap (meters)

[0115] Bg=Magnetic Flux Density (tesla)

[0116] The length of the air gap, lg, is the thickness of the precisionspacer 68 and is nominally 175 microns. For a magnet thickness 10 of 525microns this gives a load line, lm/lg, of 3. Using some publisheddemagnetizing curves for anisotropic sintered neodymium-iron-boron, andthe load line of 3.0, gives a B_(g) in excess of 1.10 tesla in the airgap.

CONCLUSIONS, RAMIFICATIONS, AND SCOPE

[0117] Accordingly, the reader will see that the Variable SpeedIntegrated Planer Motor Assembly of this invention, has shown anddemonstrated;

[0118] A integrated planer stator assembly that combines the motorsstator coils, biased MR sensors and the control IC into a single partusing existing high volume semi-conductor manufacturing processes;

[0119] A simple but precise parallel rotor-stator assembly having auniform and small air gap that maximizes the magnetic flux density inthe air gap.

[0120] Rotor and stator assemblies with low reluctance magnetic returns.

[0121] Precise and variable speed operation up to 20,000 RPM.

[0122] Thick spiral stator coil conductors for maximum number of turnsand low resistance.

[0123] Biased MR sense elements precisely located relative to the spiralstator coils.

[0124] An automated and precise assembly of the rotor assembly to thestator assembly using a precision spacer to establish the motor air gap.

[0125] A simple and precise speed control digital IC that interfaces, ona serial bus, to a host system that controls the motors speed anddirection.

[0126] While my above description contains many specifications, theseshould not be construed as limitations on the scope of the invention,but rather as an exemplification of one preferred embodiment thereof.Many other variations are possible. For example the stator assembly canbe made on substrates on different materials and shapes, use othersemi-conductor processes, use different MR materials, use other controllogic and IC's, etc; the rotor assembly can be made with differentpermanent magnets and the air gap set in other ways than a precisionspacer, etc.

[0127] Accordingly, the scope of the invention should be determined notby the embodiments illustrated, but by the appended claims and theirlegal equivalents.

I claim:
 1. A variable speed integrated planer motor assemblycomprising: a. a planer stator assembly having a plurality of statorcoils made with variable width conductors fabricated by an advancedphotolithography process, b. said planer stator assembly also having aplurality of biased magnetoresistive elements precisely located relativeto the stator coils, c. said planer stator assembly having a pluralityof conductors for connecting the stator coils and the magnetoresistiveelements to the motor controller integrated circuit, d. said planerstator assembly having a motor controller integrated circuit to providevariable speed operation, e. a rotor assembly having a planer surfaceconsisting of a high energy permanent magnet and a magnetic returnstructure, f. said rotor and planer stator assemblies assembled togetherwith a precision washer to establish the motors air gap.